The present invention relates to water-soluble fiber and a method for manufacture thereof.
Among the water-soluble fibers heretofore known is polyvinyl alcohol fiber which is generally fabricated into a twisted yarn, woven fabric or non-woven fabric and put to use in a diversity of applications. For example, it has been used for provisional reinforcing or adhesion in a variety of industrial processes.
However, polyvinyl alcohol fiber is not readily soluble in water and requires heating to at least about 80xc2x0 C. for dissolution, thus being poor in workability. Moreover, when exposed to a temperature over 100xc2x0 C., it undergoes crosslinking so that dissolution is often made difficult.
The object of the present invention is to provide a water-soluble fiber which is tough and readily soluble in water at ambient temperature and does not suffer losses in water solubility on exposure to heat and a method for manufacturing the fiber.
The present invention is directed to a water-soluble fiber composed of a high molecular compound with a weight average molecular weight of not less than 10,000, which high molecular compound is obtainable by reacting a polyalkylene oxide compound, which is obtainable by addition polymerization of an ethylene oxide-containing alkylene oxide and an organic compound containing two active hydrogen atoms, with a polycarboxylic acid, an anhydride thereof, or a lower alkyl ester thereof, or a diisocyanate compound.
The manufacture of said water-soluble fiber comprises spinning said high molecular compound.
The polyalkylene oxide compound as a major starting material for the high molecular compound of the present invention is preferably a compound having a weight average molecular weight of not less than 100 and can be prepared by addition polymerization of an ethylene oxide-containing alkylene oxide and an organic compound containing two active hydrogen atoms.
The organic compound containing two active hydrogen atoms includes, inter alia, ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,6-hexanediol, bisphenol A, aniline and so on.
The ethylene oxide-containing alkylene oxide includes, inter alia, ethylene oxide and mixtures of ethylene oxide with propylene oxide, butylene oxide, styrene oxide, xcex1-olefin oxides, glycidyl ethers and so on.
The addition reaction of such an alkylene oxide can be carried out in the known manner, and the mode of addition polymerization of ethylene oxide and other alkylene oxides may be optionally random or block.
The polycarboxylic acid, anhydride thereof, or lower alkyl ester thereof, which is reacted with said polyalkylene oxide compound, include, inter alia, phthalic acid, isophthalic acid, terephthalic acid, sebacic acid, dimer acid, pyromellitic acid, etc., anhydrides thereof, and methyl esters, dimethyl esters, diethyl esters, etc. thereof. The preferred are dimethyl terephthalate, dimethyl phthalate, dimethyl isophthalate, dimethyl sebacate, pyromellitic anhydride and so on.
The polyester-forming reaction between said polyalkylene oxide compound and said polycarboxylic acid, anhydride thereof or lower alkyl ester thereof is preferably conducted at 120-250xc2x0 C. and 10xe2x88x924xe2x88x9210 Torr.
The diisocyanate to be reacted with said polyalkylene oxide compound includes, inter alia, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, 4,4xe2x80x2-methylene-bis-(cyclohexyl isocyanate) and so on.
The urethane-forming reaction between said polyalkylene oxide compound and said diisocyanate is conducted by mixing the starting compounds in an NCO/OH ratio of, for example, 1.5 through 0.5 and heating the mixture at 80 to 150xc2x0 C. for 1 to 5 hours.
A high molecular compound obtained by reacting a polyalkylene oxide compound with a diphenylmethane diisocyanate has a tendency to be insoluble in water for the following reason.
When preparing a polyalkylene oxide compound, an alkaline metal hydroxide is used, which is usually neutralized with organic acid to give an alkaline metal salt of organic acid. When the polyalkylene oxide compound is reacted with diphenylmethane diisocyanate without removing the salt, a high-molecular compound which is insoluble in water is obtained as the salt works as a catalyst for gelation.
In order to obtain a water-soluble compound, a retardant to inhibit the gelation is employed for the reaction of the polyalkylene oxide compound with diphenylmethane diisocyanate.
The weight average molecular weight of the high molecular compound according to the present invention is not less than 10,000. If the molecular weight is less than 10,000, the fiber will not be sufficiently high in mechanical strength, giving rise to yarn breakage in the spinning process.
This high molecular compound can be processed into fiber by any known relevant technique such as melt-spinning, dry spinning, wet-spinning, etc., although the melt-spinning process is preferred if only from economic points of view.
In the melt-spinning process, the high molecular compound is melted at 50-200xc2x0 C. in a nitrogen gas atmosphere and extruded from the conventional spinning nozzle.
In this process, such additives as a plasticizer, lubricant, stabilizer, colorant, filler, etc. can be added. According to the intended application, a perfume, fungicide, agrochemical, fertilizer, etc. can also be incorporated.
The water-soluble fiber as spun has large elongation. For example, the elongation of a fiber with a diameter of 10 xcexcm to 5 mm is approximately 500 to 3,000 percent.
After spinning, the fiber may be treated with a sizing or bundling agent in the hydrocarbon series or stretched. When it is stretched in a draw ratio of 5 to 30, its tensile strength is remarkably increased. The stretching may be performed concurrently with spinning.
The fiber thus obtained is subjected to various processings such as twisting and cutting. The fiber can also be constructed into mixed fabrics with other fibers.
The water-soluble fiber according to the present invention is not only high in elongation and tensile strength but is readily soluble in water. Moreover, this water solubility is not appreciably affected by heating. Therefore, as processed into a thread or yarn or a web, the fiber remains tough and self-supporting in application and, yet, can be completely dissolved out swiftly as needed. In this and other ways, this material can contribute to rationalization of various industrial processes.
The following examples and comparative examples are further illustrative of the invention, it being to be understood, however, that the invention is by no means limited thereto but limited only by the claims appended hereto.